Sophisticated brain imaging techniques show that when storing and accessing memories, individuals who carry a genetic variant linked to a heightened risk of Alzheimer Disease "activate" brain functions differently than do non-carriers, even when no outward signs of disease are present, according to a study reported in the November-December issue of the American Journal of Geriatric Psychiatry (AJGP).
The study by investigators at Columbia University is one of two in the current issue of the journal offering new evidence that brain imaging technology known as positron-emission tomography or PET scans has the potential to play an increasingly prominent role in the study and treatment of Alzheimer Disease (AD).
The second report, from researchers at Baycrest Centre for Geriatric Care, the Centre for Addiction and Mental Health PET Center and the University of Toronto, describes an advance in using PET scans to detect the presence of brain deposits known as beta-amyloid plaques, which are believed to be a telltale sign of the disease.
While it is interesting to know that there is a difference in brain function of elderly people who have a genetic variant for Alzheimer's it is the second report that is especially interesting. The ability to detect beta amyloid plaque build-up before Alzheimer's Disease symptoms become noticeable has a couple of uses. First of all, the ability to study the progression of plaque build-up will make it easier to measure the effectiveness of intervention therapies aimed at removing or stopping the build-up of plaque.
Scarmeas said the above conundrum could be solved if the PET scans could be paired with tests that would offer some biological evidence of the disease. That's why he's intrigued by another study in this same AJGP issue in which a team headed by Nicolaas Verhoeff, M.D., Ph.D., from the Kunin-Lunenfeld Applied Research Unit at Baycrest Centre for Geriatric Care, the PET Centre at the Centre for Addiction and Mental health, and the University of Toronto, reports that it successfully used a novel PET scan technique to detect beta-amyloid plaques, one of the brain lesions linked to AD. Thus, now we may be able to explore which are the earliest changes that could be detected in AD: changed brain functions during "active" memory processing or deposition of brain chemicals linked to AD.
As it now stands, doctors have no laboratory tests they can use for confirming the existence of AD or for monitoring its progression. Diagnosis is confirmed only after a relatively clear set of symptoms appears. However, autopsies of AD victims have revealed abnormally high levels of what are known as beta-amyloid plaques. Some scientists believe beta-amyloid plays a central role in AD-related brain damage. They also suspect that abnormally high levels of the substance begin accumulating in the brains of AD patients long before symptoms appear. But they have lacked a reliable test for detecting amyloid build-up.
Verhoeff and his colleagues recruited five AD patients and six healthy volunteers. All were injected with a new compound designed to cross from the bloodstream into the brain, attach itself to amyloid deposits and then send out harmless radioactive signals that can be detected with a PET scan. This new compound, which had been originally developed at the University of Pennsylvania in collaboration with the Centre for Addiction and Mental Health PET Centre in Toronto, was compared to another compound that had been developed independently at the University of Pittsburgh. What the study found is preliminary evidence that the new compound or "tracer" may also be effective at allowing the researchers to use PET scans to discriminate between amyloid levels one would expect to see in AD versus non-AD patients.
Currently if a doctor could tell you that you have beta amyloid plaque build-up there is probably not much you could do in response except perhaps to follow any dietary advice gleaned from population studies of Alzheimer's Disease risk. However, eventually effective treatments will be developed to reverse beta amyloid plaque build-up. If the treatments have no side-effects and are easy to deliver then everyone may decide to get treated periodically as they get older. However, if the treatments are difficult to administer (e.g. injection of antibodies into the brain) or carry some risk (e.g, a vaccine that occasionally causes brain inflammation) it would be better to get a PET scan to test for the presence of plaque build-up. Then only those with plaque build-up could get treated.
In the short to medium term a PET scan technique that can detect beta amyloid plaque build-up is going accelerate scientific research. For scientists trying to understand AD progression and testing methods of intervention against it the ability to measure plaque levels will be quite valuable. Every advance in the ability to watch internal biological processes whether normal processes or disease processes, makes it easier to understand and manipulate those processes.
|Share |||Randall Parker, 2004 November 10 06:53 PM Biotech Assay Tools|